This invention concerns a device to cool the rolling rings in a rolling stand for long products, and the method performed with the device.
The invention is applied in co-operation with rolling stands used to roll long products such as bars, round pieces, wires or profiles in general.
The state of the art provides cooling systems associated with rolling stands and predisposed to deliver jets of a cooling fluid, normally water, onto the surface of the rings or working rolls of the stands. It is well-known that the over-heating of these surfaces, caused by the repeated rolling passes in contact with the hot surface of the product to be rolled, generates premature wear on the rings-rolls and rolling conditions which are not ideal.
Normally, therefore, cooling systems are provided comprising nozzles to deliver fluid mounted on collectors arranged in co-operation with the periphery of the rings.
The collectors are mounted fixed on the housing of the stand, at a certain distance from the surface to be cooled, and are arranged so as to cover, with the relative delivery nozzles, a part of the circumference of the rings-rolls.
One problem deriving from using such systems is that, due to the fixed position of the collectors, the distance between the delivery nozzles and the surface to be cooled is modified every time that the rolling rolls are adjusted to define a different gap value.
Moreover, it is well-known that the rolling rings are subjected to periodic operations of surface re-working to restore the geometric shape of the rolling channels which deteriorates and deforms due to the wear induced by the rolling passes.
Each of said re-working operations causes a reduction in the diameter of the ring, which can be as much as 15-20% with respect to its original value before it is necessary to replace it.
The modification in the distance between the nozzles and the surface to be cooled, due to the reasons explained above, causes a variation in the cooling conditions, which depend mainly on the flow rate of water and pressure of impact against said surface.
Since the pressure of impact rapidly diminishes as the distance from the delivery point increases, with approximately a quadratic function, it is obvious that even a small modification of the distance entails high variations in the cooling parameters. The fact that cooling depends on the working conditions causes serious operating disadvantages since it does not make possible to guarantee a sure control of the temperature of the rings and therefore reduces the efficiency and reliability of the cooling system.
Moreover, the non-ideal working conditions of the rolls, which may be subject to overheating caused by ineffective cooling, cause a premature wear thereon with a consequent reduction in their average working life.
Another disadvantage is that, due to the variable distance between the nozzles and the surface to be cooled, uncontrolled sprays of cooling fluid may be generated which hit the whole stand.
Documents JP-A-60-199504, U.S. Pat. No. 4,974,437, JP-A-04-046613, JP-A-01-254303 and JP-A-54-083658 disclose all cooling devices in rolling stands for plane products such as strips or sheets; these cooling devices comprise nozzles which are solid with the chocks and are placed along a line which is parallel to the axis of the relative rolling roll.
These devices cannot be efficiently applied to cool, in an effective and uniform way, the surface of rolling rings or rolls in rolling stands for long products, because the relative nozzles are not placed around a substantial part of the surface of these rolls.
DE-C-913.044 discloses a cooling device for rolling rings or rolls in a rolling stand for long products, in which the nozzles are placed on a tube parallel to the axis of the ring or roll; this tube is not solid with a relative chock and does not follow the movements of the chock during shifting or gap control.
The present Applicant has devised, tested and embodied this invention to overcome these shortcomings and to obtain further advantages.
The invention is set forth and characterized in the respective main claims, while the dependent claims describe other characteristics of the main embodiment.
The purpose of the invention is to achieve a cooling device for rolling rings in rolling stands for long products, and the relative method, such as to ensure efficient and constant cooling conditions even when there is a variation in the working parameters, such as those caused by a modification to the gap between the rolls or those caused by variations in the diameter of the rolls generated by re-working and grinding.
To be more exact, the purpose of the invention is to guarantee that the distance between the surface of the ring and the point where the cooling fluid is delivered by the relative delivery means is substantially constant; this is to ensure, once the desired parameters have been set, that efficient cooling conditions are maintained.
The cooling device comprises a plurality of curved collectors arranged around and in cooperation with a substantial part of the circumference of the rolling rolls.
Each of the collectors is able to support a plurality of delivery elements, such as nozzles, apertures or similar, facing towards the surface to be cooled and suitable to deliver a jet of cooling fluid onto said surface.
According to one characteristic of the invention, the collectors are mounted on a support solid with at least a chock of the relative roll.
In this way, with every new adjustment of the gap between the rolls, and consequent modification to the reciprocal position of the chocks, the collectors are displaced together with the chocks, so that their position with respect to the surface of the rolls remains substantially constant for any value of the gap.
According to another characteristic, the collectors are interchangeable with other collectors which are identical except that they have a different size, correlated at least to the different diameter of the rings/rolls.
According to a variant, the collectors can be displaced in a controlled manner towards the surface of the roll and with respect to their fixed support which is solid with the relative chock.
Therefore, every time the rolls/rings are removed for surface re-working and grinding, with a consequent modification to their diameter, the collectors are either replaced by others with a different size, or their assembly position is modified, so as to guarantee that the distance between the surface of the roll and the point where the cooling fluid is delivered remains substantially constant.
According to a variant, the position of the collectors can be modified so as to vary, or also vary, the intensity of the cooling to the surface of the rolls.
In a first embodiment, the position of the collectors is adjusted by a mechanical adjustment to their assembly position on the relative support and with respect to the surface of the roll. In another embodiment, the adjustment is made substantially automatically by means of positioning actuators which are associated with said support and can be remote commanded.
In a further embodiment, the adjustment to the position of the collectors is made by means of a control unit able to manage the functioning of the rolling stand; when the rolls have a new diameter value after grinding and/or according to the gap value set, the control unit automatically adjusts the position of the collectors to guarantee that the distance between the nozzles and the surface is constant.
In a further evolution, the collectors, or at least some of them, can be translated along the relative support in a direction substantially parallel to the axis of the rolls, so that they can be centered with respect to the rolling channels affected by the passage of the rolled stock.
According to a first embodiment, the collectors are translated mechanically; according to a variant, they are translated automatically by means of actuators associated with a control unit.
According to the invention, on the outer part of the support on which the collectors are mounted, there are fitting elements by means of which the collectors are connected to flexible conduits able to feed the cooling fluid to the delivery nozzles. By using flexible conduits it is possible to displace the collectors towards the surface of the rolls and/or parallel thereto without entailing problems in the feed of the cooling fluid.
Using the invention guarantees that the distance between the delivery nozzles and the surface of the rolls is constant, and thus ensures efficient and constant cooling conditions even when the working conditions of the rolls themselves varies.
This also gives an increase in the average working life of the roll. Moreover, the fact that the distance between the delivery nozzles and the surface of the rolls is constant prevents the stand from being hit by unwanted sprays of cooling fluid.
A further advantage is that the flexible conduits are arranged and extend outside the support of the collectors and therefore are in a position protected from overheating and knocks or mechanical damage.